Where the search for "keyword" doesn't have that many pages. To make matters even more confusing, the page is linked from another instance like this - same link structure, another 404, where the page is higher than the search goes to. Sorry if that's confusing!

I am using the plugin WP Pagination, not sure if that is causing it. I have this plugin on other sites which don't have these errors, so I don't think it is, but could still be related.

Has anyone ever seen this before? It's just so bizarre... neither the linked page, nor the linked-from page exist... so how are these 404s even happening??